This invention relates to a frame number converter of a television signal. Such a television signal frame number converter is particularly useful in a television standard converter.
The NTSC system, the PAL system, and the SECAM system are well-known as television standards widely adopted in the world. When it comes to convert television standards, from the NTSC system to the PAL system for example, it is necessary to convert the signal having 30 frames per second to the signal having 25 frames per second.
Generally, a television signal frame number converter has a frame interpolation process, carrying out by using two successive frames of one television standard signal, and converting them into another standard signal in accordance with an interpolation coefficient.
It is obvious that an interpolation coefficient is closely related to a timing of two standard signals at an interpolating time, and varies with a lapse of time.
However, the conventional method for determining an interpolation coefficient is a stereotyped one. The interpolation coefficient has been determined by a nominal timing ratio of the two concerning television standards. Taking the NTSC system and the PAL system for instance, the PAL system's 5 frames can be processed from the NTSC system's 6 frames, using constant coefficients of 1.0, 0.8, 0.6, 0.4, and 0.2 for each, if the NTSC system and the PAL system have exact 30 and 25 frames per second, respectively.
In reality, the frame numbers of each television standard signal deviates from its nominal value, furthermore, the NTSC's real frame numbers are not equal to 30 but 59.940052/2. The difference between the nominal coefficient value and real one makes the degradation of the converted signal in picture quality.
In order to obtain the converted signal having a good picture quality, it is desirable to determine the interpolation coefficient in real time.